Revert "gha: add hosts file workaround for Windows localhost resolution"

This reverts commit eed32b752b.

Windows's Winsock getaddrinfo does not consult the hosts file for
"localhost" because an internal hard-coded rule short-circuits first,
so the Add-Content step had no effect on the failing tests. Remove
the ineffective workaround now that a skip guard replaces it.

Co-authored-by: Claude <noreply@anthropic.com>

.github/workflows/build.yml

@@ -38,12 +38,6 @@ jobs:
         run: ruby -v
       - name: Compiler version
         run: ${{ env.CC }} --version
-      - name: Ensure localhost resolves on Windows
-        if: runner.os == 'Windows'
-        shell: pwsh
-        run: |
-          Add-Content -Path $env:WINDIR\System32\drivers\etc\hosts -Value "127.0.0.1 localhost"
-          Add-Content -Path $env:WINDIR\System32\drivers\etc\hosts -Value "::1 localhost"
       - name: Build and test
         run: rake -m test:run:serial
 
@@ -85,11 +79,6 @@ jobs:
           persist-credentials: false
       - name: Ruby version
         run: ruby -v
-      - name: Ensure localhost resolves
-        shell: pwsh
-        run: |
-          Add-Content -Path $env:WINDIR\System32\drivers\etc\hosts -Value "127.0.0.1 localhost"
-          Add-Content -Path $env:WINDIR\System32\drivers\etc\hosts -Value "::1 localhost"
       - name: Build and test
         shell: cmd
         run: |